A lithographic printing plate precursor

Abstract

A lithographic printing plate precursor is disclosed including a support and a coating including a polymerisable compound, an optionally substituted trihaloalkyl sulfone initiator, a leuco dye and a specific infrared absorbing compound including a six membered ring in the central position.

Description

TECHNICAL FIELD[0001]The invention relates to a novel lithographic printing plate precursor.BACKGROUND ART[0002]Lithographic printing typically involves the use of a so-called printing master such as a printing plate which is mounted on a cylinder of a rotary printing press. The master carries a lithographic image on its surface and a print is obtained by applying ink to said image and then transferring the ink from the master onto a receiver material, which is typically paper. In conventional lithographic printing, ink as well as an aqueous fountain solution (also called dampening liquid) are supplied to the lithographic image which consists of oleophilic (or hydrophobic, i.e. ink-accepting, water-repelling) areas as well as hydrophilic (or oleophobic, i.e. water-accepting, ink-repelling) areas. In so-called driographic printing, the lithographic image consists of ink-accepting and ink-abhesive (ink-repelling) areas and during driographic printing, only ink is supplied to the maste...

AI Technical Summary

Benefits of technology

The present invention provides a printing plate that is based on photopolymerization and offers an excellent visual contrast during imaging. Surprisingly, the print-out image formed upon heat and / or light exposure of the coating remains stable or is even boosted after storage in office light conditions. This means that the printing plate can be stored and handled without losing its effectiveness and can even improve with time.

Problems solved by technology

Although some plate precursors are capable of producing a lithographic image immediately after exposure, the most popular lithographic plate precursors require wet processing since the exposure produces a difference in solubility or difference in rate of dissolution in a developer between the exposed and the non-exposed areas of the coating.

However, for photopolymer lithographic printing plates which are processed on-press and thus development of the plate is not carried out before mounting the plate on the press, a previous inspection and discrimination of the plate including colorants is not possible.

However, this technology is especially suitable for thermofuse plates—i.e. plates including an image-recording layer that works by heat-induced particle coalescence of a thermoplastic polymer latex,—and does not work well in photopolymer coatings.

Indeed, only an acceptable contrast in photopolymer coatings is feasible when exposed by very high laser energy and / or when a substantially high concentration of the thermochromic dye is incorporated in the coating.

A problem associated with the prior art materials is that often the obtained print-out images after exposure are characterized by only a low contrast between the exposed and the non-exposed areas, high exposure energies are required to generate a contrast and / or high levels of leuco dyes are required.

Moreover, often the obtained contrast fades away in time when the exposed plates are not immediately used for the printing job.

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